Electrostatic voltmeter.



31C. HUBBARD.

BLEGTROSTATIG VOLTMETER.

APPLICATION FILED 0012.13, 1911,

.latented Oct. 29, 1912.

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m1111111@ l@ T1- M1, ,11111111111111111111111|y M1111 f- :i 2 iLmrmznmmmmmmzr mmm ELEGTROSTATC VOLTMETER.

Specification of Letters Patent.

Patented ct. 29,1912.

Application filed October 13, 1911. Serial No. 654,444.

To all 'whom it may concern:

Be it known that l, JOHN C. HUBBARD, a citizen of the United States.rresiding at *Worcester` in the county of Worcester and State ofMassachusetts, have invented a new and useful Electrostatic Voltmeter,of which the following is specification.

The principal objects of the invention are to provide a 'voltmetcr orelectrometer of very great sensitiveness; to provide means whereby anordinary form of electroscope can, by very simple and inexpensiveadditions, be converted into a sensitive electrostatic volt-meter orelectrometer: to provide an instrument of the indicated character havinga `constant sensibilityfor a given strength of field whereby measuresupon large potentials can be made with the same absolute degree ofaccuracy as upon small potentials; to provide an instrument of thischaracter useful in all nleasureinents coinmonly made either with thegold-leaf electroscope, quadrant clectrometcr, or electrostaticvoltmcter, and which can be used for alternating current voltages aswell as for direct.

Further objects pear hereinafter.

Reference is to be had to t-he accompanyine' drawings, in whichrligure 1is a front elevation of a gold leaf electrometer constructed inaccordance with this invention; Fig. Q is a plan of the same; and Fig. 3is a diagrammatic. view showing the electrical connections.

The invention is shown in a simple form in which a stand is providedhaving levcling screws 11 for supporting the instrument. On this standis a shaft 12 to which is xed a easing 18 of conductingmaterial. rThiscasing is provided with an insulating plug 14 for supporting a mercuryterminal 15 with which is connected a gold leaf indicator 16 dependingin the casing. At the bottom the casing is provided with anadjustingjrscrew 17 which carries an insulating support 18 on which are mounted twoconducting terminals 19 insulated from each other by the support 18 andmelting an angle with each other. These are so located that under normalconditions the gold leaf 16 depends between the terminals 19withouttouohing them. A pair of springs 20 engage the terminals 1.9 andare connected through insulating plugs 21 to binding screws 22. it thesides of the casing oppoand advantages will apsite the indicator arewindows 23 through which the position of the indicator may be observedas for example through a microscope 24 supported by the shaft 1Q. Theshaft. 12 is mounted to turn in bearings on the support 10 and isprovided with a hub 25 which is engaged by a split bushing' 26 on anadjusting frame 2'?. A screw 2S is provided for clamping the splitbushing to the hub of the shaft so that any motion of the frame will betransmit-ted to the shaft. he frame is provided with an adjustii'lgscrew 280 and a spring-pressed plunger 29 both yengaging a. lug 30 caston the support 10.

The casing' 13 also provided with a disk 33 concentric with the shaftand provided with a scale 31 preferably with a Vernier 39. by which theangularity can be read.

t will be obvious that by loosening the screw 28 the casing can beturned to any de sired point and then by tightening the screw the frame27 can be adjusted to any desired degree of neness thus adjusting theposition of the casing in like degree.

rlhe principle of the instrument `depends on the fact that when theindicator is charged to a given potential the instrument may be tiltedor turned so that the force of gravity7 or some other force, constant inmagnitude and direction, acting on the indicator will balance theelectric force acting on the same in such a way that the indicator willoccupy the same position with 4respect to the other parts of theinstrument" as it did in the normal position of the instrument beforethe indicator was charged. T he potential or voltage which has beenapplied to the indicator is then proportional to the sine of the angle oof tilt.

The device is connected up as usual. The

diagram illustrates the connections The bindingscrews 22 are connectedwith the opposite poles of a battery B or the like giving the fieldplates 19 a constant potential difference. rEhe middle of the battery,screw 1'? and casing 13 are earthed The.

terminal 15 is connected with a switch S which can be connected to theearth, to a known potential, as a standard cell Vs, 'for calibration, orto the unknown potential (Vx).

ln order to use the instrument in measuring potentials it is firstnecessary to calibrate it. The case and '-'idieator are put to earthwhile the field plates 19 are put at a constant dierence of potential asdescribed. rli`he microscope or reading device of the indicator is soadjusted that the indicator stands at a delinitely measured place in thefield; for instance, when the microscope is used, the image of theindicator is seen to coincide with a cross hair or marl; at the focus ofthe eyespiecc oit the said microscope. The earth connection with theindicator is now broken, and the indicator is connected with one pole ofa. standard cell of potential VS, the other pole being to earth. ThenUsing thi-s value ot 7c it is then possible to measure arly unknownpotential by connecting it in place ot the standard cell. The unknownpotential may also be measured by direct comparison. Let VS be the'known potential, VX the unknown, o5 the angular reading for the knownpotential, and ex the angular reading for the unknown potential, thenThe theory may be stated in eral Way follows: Let the suspended orsupported in an electric field produced between the plates i9 chargedMto a deinite difference of potential. Suppose now that the indicator beuncharged or put to some definite potential which, for convert ience, Weshall call Zero, and let the position of the indicator with reference tothe plates 19, or `with reference to any bodies which produce the fieldhe measured. Call this the zero position of the indicator. Now let theindicator be charged to the potential which is to be measured. Theindicator will. be deiicctcd or turned by the electric field acting uponthe charge on the indicator. l

vmore gen indicator be ,lhe framework or case which carries thc systemof field bodies and the support of the indicator is now turnedor-rotated in such a direction that the indicator is drawn by sometorce, constant in direction and magnitude, such as the force ofgravity, back into its original position with reterence'to the field undthe system which produces it.. The iudicator is now in equilibrium underthe action of two forces, (a) the deliecting torce ci the electricfield, and (o) the restoring force, (gravity). Let ythe angle throughwhich the instrument has been turned be o. Then We have Vrie sin. o,

where Vis thc potential to bc measured, c., that applied to thcindicator, t is a constant ol thc instrument which depends upon thestrength of the field and upou the deus-ity aud structure ot theiiulicator, and is the angle through which the instrument has beenturned in order to restore the indicator to its initial position. For,consider meente any portion of the indicator, rThe torce G, which hasbeen called the restoring torce is constant in magnitude and directionand exerts the moment CLGIGQ sin. e,

when n the perpendicilar distance from the lintx ot acticn ot the torceG to the point ot' support the indicator, and r is the distance trom thepoint considered to the axis of support.

- Let the 'torce li be thc componentof the electric force acting; at thesame point perpendicular to the radius to the point from the airis ofsupport. This force is, by elec- -triral theory, prffportional to thepotentiai applied to the indicator, th` is FIKV, since by tuemanipulation of the instrument above described, the indicator is in afield ot constant strength and tix-ed direction with respect to theindicator. The momentot this force is KW7. These two moments are equaland opposite, or,

lfrGr sin. cpr-'0. Since this is truc 'tor any portion ot the lndicator1l is truc tor all. portions and we have, therefore,

i" r: KG/l) sin. cpv-:viii e,

as stated.

Although l have illustrated and described the invention as applied to agold lealc cicrtroscopc, it is to bc understood that this is donc torillustrative purposes and do not wish to limit myself thereto, but

What l do claim isl. in an electrostaticvoltmetelg the combination ot anindicator adapted to be charged and to be moved, a pair ot terminalsadapted to be connected with constant source ot .electricity to keepthem at a con staut potential dilterence forinlluencing the indicator tomove it, a casing for supporting the terminals and indicator, and meanswhereby said casing can bo moved to bring thc indicator when chargedbui-l; to the position it assumed when not charged.

2. ln a device ol the character described, the combination with. a,movable casinghot` a' support thereon, an indicator on the supportadapted to be charged and to be moved thereby, a pair ot teri'ninalscarried by the casing on opposite sides ot the indicator for connectionwith the opposite poles ot a constant source ot electricity to keep themat a constant potential difference, and means whereby the casing can bcmoved for the purpose oi" restoring the indicator to its u1u-.harmedposition by the aid of an independent torce while the indicator andterminals are charged.

3. ln a device ci" the character described, the combination oit a casinghaving a support thereon, a freely inovabie indicator carried by saidsupport, e pair of terminals insulated from each other and mounted onseid casing in position to influence the indicater when charged to causethe indicator to move, and ineens whereby said casing can be rotated onen exis for he purpose of bringing he indicator back to its unchargedposition by the aid of gravity when charged.

4. n e device of the character described, he Combination Wit-h :isupport, of a shaft supported hereon and capable of being turned byhenri, a. casino fixed to the shaft, an indicator in the casing, ineensfor eiectricaily inh'iencing the inciiooi'or, en adjush able frameconnected Wih said support mounted et one end of seid shaft, and meansfor fixing seid freine *no the shaft, whereoy the shaft can he jenrnedby -the adjustment of the frames 5. in e device of the characterdescribed, Jthe coinhinaion with e support, of a shaft Re@ to the shaft,an indicoor in the casing, means for eiectrioaiiy lninencing theindirotatobiy supporeri thereon, a easing cater, an adjustable frameconnected Wihf said suppori and mounted at one end of seid my hond, indie presence of JWo subseri..fing` witnesses.

Ul-1N C. HUBBARD,

-iVitnesses ALBERT E. F Y, C. Formeel 1i//essonE having e

